1. Field of the Invention
The present invention relates to an optical pickup including a polarization holographic optical element (HOE) and a photodetector. More particularly, the present invention relates to an optical pickup including a polarization HOE designed to effectively split light and a photodetector with a reduced number of sections to receive light transmitted through the polarization HOE.
2. Description of the Related Art
In conventional photodetectors and HOEs with complicated configurations and patterns, it is difficult to control a pickup and lower optical efficiency results from the splitting of light. A conventional optical pickup is disclosed in U.S. Patent Publication No. 2002/0159378 A1, the entire contents of which are incorporated herein by reference, and includes a polarization HOE that transmits a transversely polarized beam and splits a horizontally polarized beam into beams that are then diffracted, and a photodetector including two light-receiving portions that are split into four quadrants and two halves, respectively, and receive plus first-order diffracted beams and the other two light-receiving portions that are composed of eight sections and a single section, respectively, and receive minus first-order diffracted beams. The polarization HOE splits plus and minus first-order and zero-order diffracted beams in the ratio of 99:1. The photodetector then receives the plus and minus first-order diffracted beams to control a focusing error servo, a tracking error servo, and a tilt error servo.
Marks are created along grooves when recording a DVD-RW while marks are created along both grooves and the areas between the grooves when recording a DVD-RAM. Due to the structural difference between DVD-RW and DVD-RAM, an optical pickup in an optical recording and/or reproducing apparatus compatible with both DVD-RAM and DVD-RW discs typically employs a photodetector with a complicated configuration.
In particular, since the temperature rises above 70° C. due to heat generated by the light source and other optical elements during recording, the optical pickup performs recording at an extremely high temperature. The heat can adversely affect the ability of an optical pickup in sultry weather.
In particular, the optical length of an optical system changes and optical components suffer deviations from their normal positions under high temperature conditions. Since an optical pickup requires a larger number of optical components for recording than for reproducing, greater deviations between optical components can be tolerated. Since optical elements in an optical pickup are bonded using an ultraviolet (UV) curing adhesive, the bonded portions suffer misalignment or expansion at high temperatures, which causes a beam transmitted or reflected by the optical elements to deviate from its intended path or a focal point of the optical beam to become out of focus. This may degrade jitter characteristics. Jitter refers to an increase in the deviation of a signal detected by a photodetector caused by defects in the marks written to an optical disc or the asymmetric shape of a beam spot created on the optical disc.
To eliminate these drawbacks, there is a need for an optical pickup with a reduced number of optical elements and bonded portions as well as a simplified structure.